Finding the X-intercept of a function

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In summary, the math teacher gave the answer of plus or minus 24sqrt3. However, the student does not know how to get this answer. The student asks for help and is given the answer of 0. The student then calculates x using this answer and gets the correct solution of x=u^3.
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Airp
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Homework Statement


F(x)= x-12x1/3 Find the X-intercept

Homework Equations


X-intercept means y=0

The Attempt at a Solution


My math teacher gave plus or minus 24sqrt3 as an answer, but I have no idea how he got that! He also got 0, but I do understand that one... I just don't know how to get the 24sqrt3 Could someone help me, please?
 
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  • #2
Airp said:

Homework Statement


F(x)= x-12x1/3 Find the X-intercept

Homework Equations


X-intercept means y=0

The Attempt at a Solution


My math teacher gave plus or minus 24sqrt3 as an answer, but I have no idea how he got that! He also got 0, but I do understand that one... I just don't know how to get the 24sqrt3 Could someone help me, please?

Set ##u = x^{1/3}##, so your equation becomes ##0 = u^3 - 12 u##, or ##0 = u(u^2-12)##.
 
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Thank You! Quick question: since you put everything to the cube, should you put -12 also to the power three, because that's how I finally got the answer! Thank you so much!
 
  • #4
The u-substitution is all you need. However, the answer you get is for u. x = u^3. So you will cube your answer.
There should be no reason to cube 12. That would be assuming that
##F(x)^3=(x-12x^{1/3})^3 = x^3 - 12^3 x## but that is not how powers of polynomials work.
Edit:
However, in this case, since you are assuming that F(x) = 0 (x- intercept), you will get the right solution since:
##0=x-12x^{1/3}##
##x=12x^{1/3}##
##x^3=12^3x##
##0=x^3-12^3x##
There are many ways to get to the answer...just be sure you know why you are doing things.
 
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  • #5
RUber said:
The u-substitution is all you need. However, the answer you get is for u. x = u^3. So you will cube your answer.
There should be no reason to cube 12. That would be assuming that
##F(x)^3=(x-12x^{1/3})^3 = x^3 - 12^3 x## but that is not how powers of polynomials work.
Edit:
However, in this case, since you are assuming that F(x) = 0 (x- intercept), you will get the right solution since:
##0=x-12x^{1/3}##
##x=12x^{1/3}##
##x^3=12^3x##
##0=x^3-12^3x##
There are many ways to get to the answer...just be sure you know why you are doing things.
Thank you so much! This community really is awesome!
 

Related to Finding the X-intercept of a function

1. What is the x-intercept of a function?

The x-intercept of a function is the point where the graph of the function crosses the x-axis. It is the value of x where the function's output, or y-value, is equal to zero.

2. How do I find the x-intercept of a function?

To find the x-intercept of a function, set the function equal to zero and solve for x. This will give you the x-coordinate of the intercept point. You can also graph the function and visually determine the x-intercept by locating where the graph intersects the x-axis.

3. Can a function have more than one x-intercept?

Yes, a function can have multiple x-intercepts. This occurs when the function crosses the x-axis at more than one point. In some cases, a function may not have any x-intercepts if the graph does not intersect the x-axis.

4. What does the x-intercept tell us about a function?

The x-intercept provides information about where the function crosses the x-axis, which can be useful for analyzing the behavior of the function. It can also be used to find the roots or solutions of the function, as the x-intercept corresponds to the input values where the output is equal to zero.

5. Is there a difference between the x-intercept and the root of a function?

No, the x-intercept and the root of a function are the same thing. Both terms refer to the x-value where the function's output is equal to zero. However, the term "root" is often used in the context of solving equations, while "x-intercept" is used in reference to graphing a function.

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